What does Exodus 12:26 mean?

For Yahweh will pass through to strike the Egyptians; and when he sees the blood on the lintel, and on the two door posts, Yahweh will pass over the door, and will not allow the destroyer to come in to your houses to strike you.

You shall observe this thing for an ordinance to you and to your sons forever.

It shall happen when you have come to the land which Yahweh will give you, according as he has promised, that you shall keep this service.

that you shall say, ‘It is the sacrifice of Yahweh’s Passover, who passed over the houses of the children of Israel in Egypt, when he struck the Egyptians, and spared our houses.’” The people bowed their heads and worshiped.

The children of Israel went and did so; as Yahweh had commanded Moses and Aaron, so they did.

At midnight, Yahweh struck all the firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the captive who was in the dungeon; and all the firstborn of livestock.